1. Field of the Invention
The invention relates to a method of controlling a switching flap, and a switching-flap actuating unit.
2. Description of Related Art
Switching flaps are arranged in intake pipes which are connected with cylinders of an internal-combustion engine. Such an air intake duct system is, for example, known from DE 196 14 474. The air intake duct system described therein comprises a helical air intake duct for each cylinder. The air is taken in via a central collective inlet duct arranged inside the helical intake ducts. Air is taken in via the collective inlet duct shared by all air intake ducts and routed via the individual air intake ducts to the cylinders of the internal-combustion engine. For changing the length of an air intake duct, a short-circuit duct is provided which is adapted to be opened and closed with a switching flap. In the air intake duct system described in DE 196 14 474 the individual switching flaps are connected with each other via a common shaft. Further, a plurality of switching-flap shafts may be provided, in particular one switching-flap shaft per switching flap. In addition, air intake duct systems are known where the air intake ducts do not extend helically about a collective inlet duct but, in particular in an in-line engine, extend parallel to each other. Here, the shape of the air intake ducts is, for example, adapted to the external circumstances, in particular the space available. For varying the length of the air intake duct, such air intake duct systems comprise switching flaps which are connected with a switching-flap shaft. The common switching-flap shaft or the individual switching-flap shafts is/are connected via a worm gear with a gearwheel segment, i. e. a circular segment of a gearwheel. The gearwheel segment is connected with the switching-flap shaft which supports one switching flap or a plurality of switching flaps. Here, the gearwheel segment serves as a stopper such that two end positions of the switching flap are defined.
Such switching-flap actuating units have the drawback that the gearwheel segment may get stuck in the end positions. Further, damage to the switching-flap shaft or the switching flap itself cannot be detected. In particular, it is not possible to check the operability of the switching flap. In addition, tearing-off of the switching-flap shaft cannot be detected. Thus the safety standard OBD 2 is not complied with.
For detecting a breakage of the switching-flap shaft, it is known from DE 102 15 927 that the shaft is provided, in longitudinal direction, with an electric conductor to which a potential is applied. In the case of shaft breakage, the electric conductor breaks either, such that due to the change in potential the breakage of the shaft can be detected. Here, the electric contact between the conductor and an evaluation means is established by electrically conducting bearing bushes. Consequently, a shaft breakage occurring outside the bearings, or damage to the shaft hub and/or the junction between the switching-flap shaft and a worm gear cannot be detected.
Further, switching-flap actuating units pose the problem that the location of the individual components must be exactly defined for installation purposes. This is in particular difficult when the actuating unit has been removed for the purpose of being subjected to a functional test.